In their most rudimentary form, automotive engine mounts comprise no more than a block of elastic material, such as rubber, provided with threaded bolts facing in substantially opposite directions for connecting an engine to a frame. Such mounts, beyond their inherent elasticity, are incapable of absorbing excessive engine movements, and since engines do not always run smoothly, movements generted by them are simply transferred to the automotive frame or, in the worst case, cause rupture of the elastic component of a mount. In any event, such mounts may be the source of considerable irritation to the motorist. They are not compatible with modern notions or motoring comfort. They may, however, contribute significantly to the deterioration of automobiles.
It is, therefore, not surprising that the industry has sought to improve the performance, i.e., the absorptive characteristics of engine mounts. This has led to the development of so-called hydraulic engine mounts. Hydraulic engine mounts usually comprise a core or support, for attachment to an engine, and a base or anchor for connection with the frame of an automobile. Core and base may be connected by an elastic element, but the operativeness of such mounts resides in the fact that they are additionally provided with at least two elastically deformable chambers filled with a fluid and separated from each other by a diaphragm mounted for limited movement and/or provided with a throttle, to permit an exchange of fluid between the chambers in response to relative movements between the core and the base. Broadly speaking, the capability of such mounts of absorbing or dampening relative movements between core and base is a function of the elasticity of the chambers and of the capacity of the throttle.
Such mounts are known from West German Pat. No. 28 02 896, for instance. They may yield a favorable motion transfer function for an adjustable range of frequencies, based on their parameters. Except for their static stiffness, the transfer function of such mounts initially decreases with increasing frequencies to a minimum value and then increases to a maximum value in the resonant range. Further increases in frequency again lead to decreased transfer characteristics which lie, however, above the level of the static stiffness. Maximum absorption is obtained near the initial minimum value.
Another type of hydraulic engine mount incorporating an absorptive mass is known from West German Pat. No. 29 47 018. The transfer function of this type of mount initially increases from a static stiffness to the resonant frequency; thereafter it drops to an absorptive value and finally it approaches an asymptotic value of final stiffness below the static stiffness. This mount is based upon the principle of moving the point of absorption proportionally to the revolutions of the engine and provides for the possibility of controlling the characteristics of the mount.
These mounts are to some extent of satisfactory performance; nevertheless, there is a need for further improvements.
Thus, it is an object of the invention to provide a hydraulic engine mount of improved motion transfer characteristics.
Another object of the invention is to provide an improved hydraulic engine mount, the parameters of which may be selectively variable.
A further object of the invention is to provide an improved hydraulic engine mount which incorporates the advantageous features of prior art mounts without suffering from their disadvantages.
It is yet another object of the invention to provide an improved hydraulic engine mount having an absorptive mass which may be selectively connected and disconnected.
An object of the invention also resides in providing a hydraulic engine mount having a frequency response which is variable in dependence of engine movement.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.